Laser arrangement

ABSTRACT

The invention in question relates to a laser arrangement ( 1 ). The device includes the means ( 2, 4 ) to steer the laser beam across a reflecting body ( 3 ). The body ( 3 ) is arranged to reflect the said laser beam so that it is aimed in a surrounding space within an area that, from an instrument plane ( 11 ) of the reflecting body ( 3 ), covers at least a part of a circular revolution, as well as an angle interval approximately ±60° to the instrument plane. The device is characterized in that its steering means ( 2, 4 ) is arranged in the path of the laser beam between the laser ( 1 ) and the reflecting body ( 3 ), and is arranged to steer the laser beam, within the area, in accordance with a pre-selected direction, whereby the steering means comprises a spatial light modulator ( 2 ), whose phase-shift pattern determines the modulated angle from the modulator.

TECHNICAL FIELD

The invention relates to a laser arrangement for controlling thedirection of a beam from a laser.

STATE OF THE ART

In many applications, it is desirable to be able to aim a laser, forexample to make it sweep across large areas. Normally, the laser ismounted on a rotating table that can be swivelled to enable the laser toexecute a sweeping motion. When the laser is to be used in anenvironment subject to jolting, the rotating table's movement can becontrolled by attachment to a gyro, thereby stabilizing the laser beam.

JP 09015526 A provides an alternative arrangement featuring acone-shaped mirror asymmetrically arranged on an axle. The axle itselfcan in turn be rotated using a motor. A steadily directed laser beamhitting the surface of the mirror will, because of the asymmetry, bereflected in a direction dependent on the angle of the axle.Consequently, this arrangement allows for the possibility of sweepingthe mirror-reflected laser beam through a full 360° by rotating the axleone complete revolution.

DESCRIPTION OF THE INVENTION

According to one aspect of the invention in question, this deviceprovides a laser arrangement with the means to steer the laser beamacross a reflecting body, which is in turn designed to reflect the saidlaser beam so that it is aimed in a surrounding space within an area,which from the reflecting body covers at least a part of a circularrotation in the instrument plane, as well as an angle interval ofapproximately ±60° in relation to the instrument plane. The device ischaracterised in that the steering mechanism is arranged in the path ofthe beam between the laser and the reflecting body, and it is designedto direct the laser beam, within the area, according to a pre-selecteddirection of the reflected beam. The steering mechanism in the devicecomprises a spatial light modulator (SLM), whose phase-shift patterndetermines the modulating angle from the light modulator.

The light modulator's phase-shift pattern alters the modulating angle byshifting the phase at different points across the cross-section of thebeam by different amounts depending on the desired modulation of thebeam. For example, etched glass plates can be used for altering thephase front of a laser beam. These patterned plates are calledkinoforms.

The reflecting body can have a number of different shapes. By allowingthe laser beam to sweep across the envelope surface of a cone ortruncated cone, it is possible to reflect the laser beam in thesurrounding space within an area that from the envelope surface in theinstrument plane comprises a circular loop as well an angle interval ofapproximately ±45° to the instrument plane. This possible area ofreflection can be achieved without having to turn the laser itself.Approximately the same possible reflecting area could be obtained usingan essentially hemispherical reflecting body. This reflecting area couldbe somewhat larger by using reflecting bodies with other shapes, forexample a parabolic-shaped reflecting body, or a wide-angled lens.

It is preferable for the steering mechanism to contain some calculatingunit arranged to calculate the direction of the beam in relation to thepre-selected direction, as well as calculate the phase-shift patternsettings of the light modulator accordingly. It would also be preferablefor the phase-shift pattern to be calculated so that aiming in thechosen direction is achieved without any significant loss of strength.

The limit of the light modulator's image-update speed is about 10 kHz.It is therefore possible with the help of a spatial light modulator todirect the laser beam in up to 10,000 directions per second anywherewithin the above-mentioned area. Using a spatial light modulator meansthat none of the device's components contain any moving parts,facilitating a very long life expectancy for the device, and lowmanufacturing and maintenance costs.

By using the light modulator above, it is possible to steer the beam insuch a way so as to inhibit the occurrence of beam divergence at thereflecting body. The calculating unit is arranged to instruct the lightmodulator to reshape the laser beam's wave front so as to avoid theoccurrence of beam divergence.

For applications in environments exposed to movement and vibration, itcan be of considerable advantage if the laser, light modulator andreflecting organ are all firmly fixed in a system together with amovement-detection device, such as a gyro. In this embodiment, oncalculating the beam direction, the steering mechanism is designed tocompensate for movement in the system detected by the gyro. The systemcan therefore be stabilized without the need for moving parts such as arotating or stabilizing table. This produces considerable cost savingsin design, manufacture and maintenance.

SHORT DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatical representation of an example of a systembased on the invention.

FIG. 2 is a diagrammatical representation of an alternative system, alsobased on the invention.

FIG. 3 illustrates an example of a mirror inserted into the system shownin FIG. 1.

FIG. 4 illustrates an example of a receiver for the system shown in FIG.1.

EXAMPLES OF THE EMBODIMENTS

In FIG. 1, the laser is denoted by the number 1 and the spatial lightmodulator SLM placed in the path of the beam 12 from the laser 1 by thenumber 2. A mirror, denoted by 3, is placed in such a way as to make itpossible to guide the laser beam across it via the SLM 2. In thisexample, the mirror 3 is designed as an envelope surface of a circulartruncated cone. The laser 1, SLM 2 and mirror 3 are firmly fixed at adefined distance to each other, so as to negate any movement in relationto one another. Thus, the beam from the laser 1 always hits the SLM 2 atthe same angle. It ought to be pointed out that the term laser radiationhere refers to both an unbroken flow of light and a pulse.

The design of an SLM 2 will not be discussed in detail here, but some ofits important features ought to be mentioned for the sake ofunderstanding. The SLM can be used to alter the phase of the laser lightperpendicular to the longitudinal direction of the beam in order tofocus, defocus or alter the beam in another way. An important feature isthat the wave front in the beam that hits the SLM 2 can be directed awayat an angle other than that obtained by reflection at the SLM's 2surface. It has been shown that it is possible to angle, or direct beamsup to 30° away from the planned reflection direction through alteringthe phase in the beam. In this way it is possible to direct the laserradiation from the SLM 2 onto an area defined as a cone, with the SLM 2at the apex of the cone and the reflecting surface of the mirror 3 atthe bottom of the cone, the angle of inclination of the cone beingdetermined by the maximum modulation angle α used. Because the beam issteered by shifting the phase, the bulk of the incoming beam's energywill be angled away in the planned direction given by the SLM phasepattern, which will be described below. With modulating angles (α) up to30°, there is very little strength left in the laser beam. It is morerealistic at the present time to use modulating angles (α) of up to 4°,whereby very good resolution is retained. Very briefly, the angleswithin the modulated-angle area used are changed by the SLM's surfacebeing provided with a pattern (the above mentioned phase pattern) thatshifts the phase by different amounts at different points in thecross-section of the beam, depending on the desired modulation of thebeam. For example, etched glass plates can be used to alter the phasefront in a laser beam. These plates with patterns are called kinoforms.

As is evident from the above description, the cone-shaped mirror 3 isplaced with its truncated top in the middle of the beam 9 to counteractany undesirable refection in the SLM's 2 surface. In one example, at thetop of the truncated cone 10, there is a light trap in the form of alaser-light absorbing material for absorbing the undesired reflection.With the mirror's reflecting envelope surface placed symmetricallyaround the undesirable reflected beam pathway 9, reflection in themirror's envelope surface according to the predetermined pattern is madepossible by directing the beam from the SLM. For example, the beam fromthe SLM is aimed so that it hits the envelope surface along a radius 11in such a way that the beam reflected from the mirror sweeps through360°, in a direction perpendicular to the mirror's axle of symmetry(equivalent to the beam path 9). Hereafter the plane that the radius 11lies on is referred to as the mirror's instrument plane. Depending onthe SLM's maximum modulating angle (α), and the mirror's surfaceenvelope gradient and distance in relation to the SLM, the beam can evenbe made to sweep upwards and downwards in relation to the mirror'sinstrument plane. With the cone-shaped mirror in FIG. 1, it is possiblefor the beam to sweep upwards and downwards about ±45° in relation tothe instrument plane. When a very short cone is used, the beam isallowed to sweep upwards and downwards only a few degrees from theinstrument plane. In a further case, using a cone partitioned along themirror's symmetrical axis, it is possible for the beam to sweep through,for example, 180° or 90°.

A calculating unit 4, for example a personal computer (PC), is connectedto the SLM 2 and is designed to influence the setting of the SLM's 2phase pattern. The PC 4 is equipped with software for enteringinformation from a user for directing the laser beam either at a targetin space (for example, given by its co-ordinates), or in a directioninto space (for example, by means of angles). The software containsinstructions for calculating how the beam from the SLM 2 should be aimedso as to achieve a reflected beam, directed according to the user'sinput, as well as the instructions for setting the phase pattern of theSLM accordingly. For specialists in the field, it is obvious how thesecalculations are done, and how they could be implemented in thesoftware. When long sequences of information are entered, for examplewhen aiming the laser beam at several targets one after the other, orwhen making the beam carry out sweeping movements across an area, it ispossible to update the direction of the mirror-reflected beam with ahigh level of frequency. As it is currently possible to run the SLM witha image-update speed of at least 10 kHz (i.e. 10,000 phase patterns persecond), it is possible to update the beam's modulating angle (α) fromthis with a frequency of up to 10 kHz, as long as the capabilities ofthe PC and/or interface between the PC and SLM is sufficiently high.

Where the PC's capacity does not accommodate real-time calculations ofthe phase pattern's appearance for each angle, then the phase patterncan be calculated beforehand for a number of angles, from which theintermediate positions can be interpolated in real time. It should beremembered that a given phase pattern in an SLM only directs the laserlight effectively within a certain wavelength. Different laserwavelengths require therefore that different phase patterns becalculated.

In one example, the PC 4 contains programme instructions designed toinfluence the light modulator to reshape the laser beam's wave front inorder to avoid beam divergence occurring on reflection in the mirror.Experts in the field will easily understand how these instructions canbe implemented.

In the example shown in FIG. 1, the laser 1, the SLM 2 and the mirror 3are all fixed in a system together with a gyro 5. The PC 4 is connectedto the gyro 5 and set up via an interface (not shown) to receive datarelating to movements in the system via the gyro. On calculation of theSLM settings, movements in the system are therefore detected andcompensated for, so that the beam from the system is aimed at the givenpoint in space, regardless of the system's movement. It is clear to anexpert in the field how this could be implemented in the software.

In the example shown in FIG. 1, the mirror 3 is designed as a truncatedcone. Experts in the field would easily recognise that mirrors shaped ina number of other ways would also be able to be used, without fallingoutside the framework of the invention as stated in the accompanyingclaims, for example the hemispherical mirror 3 in the example shown inFIG. 2. As described above, even mirrors whose reflecting surfacesconstitute part of a circular revolution—such as a semi- or a quartercircle-are included. As mentioned earlier, it is possible by means of amirror shaped like a cone's enveloping surface, to reflect the laserbeam into space within an area defined by the mirror's instrument planeand an angle interval of about ±45° in relation to the instrument plane,and whose length is determined by the strength of the laser's light. Itwould be possible to achieve about the same reflecting area with ahemispherical mirror 3. It would also be possible to manufacture otherreflecting mirrors or lenses, whose shapes are optimized to increase thewidth of the above-mentioned lobe.

The number 6 in FIG. 3 denotes a convex mirror, which in an alternativeembodiment is placed between the SLM 2 and the mirror 3, and is referredto here as an intermediate mirror. It is appropriate to introduce suchan intermediate mirror 6 into the system in a situation where themaximum modulated angle (α) of the SLM 2 is considered insufficient.

The above mentioned system is suitable for a wide range of applications.In one instance, it is used as a laser pointer that has the ability topoint to up to 10,000 targets per second 360° laterally, and, with awell-shaped mirror, −45° to 60° vertically. In an additional embodiment,the system is used as a large laser. It is even possible to use thesystem as a laser-based range finder or radar. For these applications,it is necessary for a receiver-sensor arrangement to be incorporated inthe system. The example in FIG. 4 shows a receiver-sensor arrangement 7mounted under the mirror 3, with the sensors 8 arranged in a ring.

Since the SLM's settings can be quickly changed, it is possible torapidly remove the beam from the system so as to deal with many targetsat the same time and/or to utilize several lasers that, for example,work at separate frequencies.

In the above-mentioned examples, the SLM is shown in a reflectingembodiment. The invention is of course not limited to this embodiment.In a transmitting embodiment of the SLM, a laser is placed directlyunder the mirror 3, with the SLM positioned between the laser 1 and themirror 3.

What is claimed is:
 1. A laser arrangement, comprising means forsteering a laser beam across a reflecting body, which in turn isdesigned to reflect the laser beam so that it is then aimed in asurrounding space within an area that, from the reflecting body and inan instrument plane lying perpendicular to an axis of symmetry of thereflecting body and intersecting a radius at which the laser beam hitsan envelope surface of the reflecting body, covers at least a part of acircular revolution, as well as an angle interval of about ±60° to theinstrument plane, wherein the steering means is arranged in a path ofthe laser beam between the laser and the reflecting body, and isarranged to steer the laser beam, within the area, in accordance with apre-selected direction of a reflected beam, whereby the steering meanscomprises a spatial light modulator, having an input for setting aphase-shift pattern, which determines a modulated angle from themodulator and wherein the steering means includes a calculating unitoperatively connected to a light modulator, and arranged to calculatethe setting of the light modulator's phase-shift pattern from thepre-selected direction.
 2. Arrangement according to claim 1, wherein thereflecting body is essentially cone-shaped.
 3. Arrangement according toclaim 1, wherein the reflecting body is essentially hemispherical inshape.
 4. The apparatus of claim 1, wherein the calculating unit isarrange to instruct the light modulator to reshape the laser beam's wavefront so as to avoid the occurrence of beam divergence at the reflectingbody.
 5. Arrangement according to claim 1, wherein the at least thelaser, the light modulator, and the reflecting body are all fixed in onesystem, together with a movement-sensing device, preferably a gyro,whereby, on calculation of the beam direction, the calculating unitoperates to compensate for movements in the system detected by means ofthe gyro.
 6. An apparatus comprising: a spatial light modulator operableto steer a laser beam in response to an input; and a reflecting bodyoperable to reflect the steered laser beam from the spatial lightmodulator; whereby the input is operable to aim the laser beam into asurrounding space within an area that covers at least a part of acircular revolution of an envelope surface of the reflecting body and anangle interval of about ±60° to an instrument plane, wherein theinstrument plane lies perpendicular to an axis of symmetry of thereflecting body and intersecting a radius at which the laser beam hitsthe envelope surface of the reflecting body and further comprising acalculating unit operatively connected to the input of the spatial lightmodulator and operable to calculate a setting of a phase-shift patternof the spatial light modulator corresponding to a pre-selecteddirection.
 7. The apparatus of claim 6, wherein the reflecting body issubstantially cone-shaped.
 8. The apparatus of claim 6, wherein thereflecting body is substantially hemispherical in shape.
 9. Theapparatus of claim 6, wherein the calculating unit is further operableto instruct the spatial light modulator to reshape a wave front of thelaser beam so as to avoid occurrence of beam divergence at thereflecting body.
 10. The apparatus of claim 9, wherein the reflectingbody is substantially cone-shaped.
 11. The apparatus of claim 9, whereinthe reflecting body is substantially hemispherical in shape.
 12. Theapparatus of claim 6, further comprising a laser source of the laserbeam and wherein at least the laser source, the spatial light modulator,and the reflecting body are all fixed in one system.
 13. The apparatusof claim 12, further comprising a movement-sensing device and whereinthe calculating unit is further operable to compensate for movements inthe system detected by the movement-sensing device.
 14. The apparatus ofclaim 13, wherein the movement-sensing device comprises a gyro.
 15. Theapparatus of claim 14, wherein the reflecting body is substantiallycone-shaped.
 16. The apparatus of claim 14, wherein the reflecting bodyis substantially hemispherical in shape.